Apparatus and method for making master spectrographic plates



Sept. 30, 1958 T. E. MORAN APPARATUS AND METHOD FOR MAKING MASTER SPECTROGRAPHIC PLATES Filed Nov. 25, 1953 III r14! 2 Sheets-Sheet. 1

ATTORNEYS.

T. E. MORAN 2,853,916

2 Sheets-Sheet 2 Sept. 30, 1958 v APPARATUS AND METHOD FOR MAKING MASTER SPECTROGRAPHIC PLATES Filed Nov. 25. 19ss gamma WMJQM 1* 50M A T TORNEYS United States Patent APPARATUS AND METHOD FOR MAKING MASTER SPECTROGRAPHIC PLATES v Thomas E. Moran, Cincinnati, Ohio Application November 25, 1953, Serial No. 394,261

9 Claims. (CI. 88-44) The present invention is directed to the art of spectroscopy and is particularly directed to a method and apparatus for preparing master spectrographic plates for use in analyzing spectrographic films taken of unknown materims.

At the present time many unknown substances are analyzed qualitatively and in addition many quantitative determinations are made by means of spectrographs. Especially in various metallurgical operations, quality control often depends upon the analysis of minute constituents by spectrographic methods. The present invention is concerned with a method of preparing master spectrographic plates for facilitating and expediting spectrograph analyses.

In order that the significance of the present invention may be more fully appreciated, a brief description will be given of the manner in which a spectrographic analysis is made. The first step in analyzing the composition of a material by means of a spectrograph involves the preparation of a photographic film or plate of the light or other radiations emitted by the unknown material when excited. The material can be excited in any of a number of ways, such as by placing it in a continuous electric are passing between two carbon electrodes. A1- ternatively, the material may be placed in the path of a high voltage spark, or if the material is in the form of a gas it may be excited in a Geissler tube. No matter how the material is excited, a portion of the radiation emitted fiom it is preferably condensed by means of a suitable lens, and is passed through a slit from which it is directed onto a dispersion grating or prism. The function of the grating or prism is to disperse the light and separate it into its plurality of component wave lengths, or spectrum lines which are then projected upon a photographic film or plate.

Each element produces a series of discrete spectral lines having wave lengths characteristic of that particular element. These lines appear not only in the visible portion of the spectrum, but in the infrared and ultraviolet regions as well. The prism or grating disperses the various lines by an amount correlated with their wave length and by properly arranging the slit, grating or other dispersing means, and the photographic plate, the wave lengths of the various spectral lines of an unknown material can be determined from the displacement of the spectral lines along the plate.

Once the wave length of a spectrum line has been determined, the particular substance responsible for that line can be ascertained. Tables have been prepared cataloging over one hundred thousand spectrum lines; these tables list both the wave length of a line and the element with which the line is associated. One means of determining the wave lengths of the spectrum lines produced on the photographic film, is to place the film in a comparator having lenses and mirrors for projecting a magnified image of the spectrographic film along side a master scale which has numbers corresponding to various wave lengths. The unknown plate is placed in a comparator and adjusted so that one of its known lines is in vertical registry with the corresponding wave length line pt the scale,

In addition to plain numerical scales, various spectrograph companies provide master plates having three or four of the brightest spectrum lines of several elements identified. When using such a plate, the spectroscopist inserts a photographic film of the unknown sample in the comparator and aligns it so that a known spectrum line on the film is in vertical registry with the corresponding line of the same element on the master plate. Other elements present in the unknown substance can then be identified by means of the spectrum lines corresponding with the known lines of the master plate.

The use of master plates is an improvement over the use of a simple scale since it eliminates part of the tedious operation of thumbing through a table to identify a particular line. Nevertheless, previously available master plates are not completely satisfactory in use. Briefly, the reason for this is that the master plates contain only three or four spectrum lines of any element and while this number of lines may be suflicient for certain limited types of analysis, it is completely inadequate for the qualitative analysis of complex substances, or for almost any sort of quantitative analysis.

More specifically, while it is conventional to use either the brightest spectral line, or the most persistent line, to identify a substance, and these are the lines identified on the conventional master plate; it frequently occurs that these lines cannot be used in a given analysis. In the first place several elements may have one or more spectral lines in common so that the presence of a particular line does not clearly indicate which of several possible substances is present. Furthermore, if a spectroscope does not have a great resolving power, several weak lines may converge and appear to be one line. In addition, the matrix of surrounding elements affects the density of the lines produced by a given element and' certain lines normally suitable for the identification of a substance may be weakened to a point where they are of considerably less intensity than other lines not usually employed.

Because of these various effects, the process of analyzing a spectrographic plate becomes quite involved. Especially when using spectrographic devices of limited dispersion, it quite often occurs that a line on an unknown plate corresponding to a particular line identified on a master plate may belong both to the element which the spectroscopist suspects is present in the sample and to another element having a coincident or closely adjacent line. Or the line in question may even be produced by the superposition of several weak or coincident lines helonging to several other substances. Consequently, it is necessary for thes-pectroscopist to check a second line identified on the master plate as belonging to the substance whose presence is suspected to see if there appears a corresponding line on the unknown plate. However, the same difiicultiesare frequently present at the second line so that in order to positively ascertain the presence of a particular element many checks and cross checks are necessary. In order to complete an analysis, it is often necessary to resort to various other techniques, such as obtaining a second plate of the unknown material by varying the excitation conditions or by varying the concentration of one of the elements. This second plate is then used in conjunction with the original plate and master plate as an aid in analyzing the unknown material.

Dilficulties also arise with the use of conventional master plates when making quantitative measurements. It has been found that highly accurate quantitative analyses can be made by utilizing the fact that higher concentrations of a material generally make brighter spectral lines, in turn forming brighter lines on the spectrographic film. However, because of the efiect of the matrix material upon the intensity of the lines produced by a given element and also because of the fact that the intensity of a spectral line varies with the electrical excitation conditions, such as voltage and power factor, the intensity, of a-line will. not in itself yield anaccurate index ofthe amount of a material present in a sample. Rather,

it is conventional to conduct quantitative analysis by means of paired, lines oran internal standard.'

Themethod by which this type ofanalysis is made is- With these dilficulties in mind, it is the principal object of the present invention to. provide means for obtaining a novel master spectrographic, plate in which substantially all of the, spectrum lines produced by a particular element, or more preferably by each of a number of elements, are marked in a characteristic manner. A master plate constructed in accordance with the present invention has a large number of spectral lines produced by one ormore known substances; each of the lines associated with. any particular element is marked so, as to be readily discernible from the lines produced by the other elements. More specifically, each of the spectral linesproduced by a given element has a blanked out portion disposed at a predetera mined position on, the line, this position being the same for each of the lines of a given element and being different from the positions'in which any of the other lines are marked.

A second object of the present invention is to, provide a simple method of preparing master spectrographic plates. By means of the present method, any spectroscopist can prepare his own master spectrographic plates in a-relatively short period of time. Moreover, his master plates will contain the spectral lines of only those elements; in which he is particularly interested; and in addition the lines can be produced by material excited under conditions similar to those under which the spectrographic plates of the unknown sample are prepared.

Specifically, the present method of producing, master spectrographic plates involves the steps ofdisposinga marking strip formed from an absorbing or deflecting material, in the path of the radiation emitted by a known sample at a. point intermediate the excitation position of the materialand the point at which the. radiation impinges upon a photographic film. As will be explained below, the marking strip can be variously located relative to the excitation means, slit, and film; however, in any position the strip extends at right angles to the slit.

After the marking strip has been positioned, a sample of a known material is excited in the spectrograph in the usual manner to produce a large number of characteristic spectrum lines on the photographic film. How- 'ever, the absorbing or deflecting strip effectively blocks out a small-portion of each of, the spectrum lines, leaving a blank area in the line. Since the absorbing strip is disposed transversely of the slit at substantially right angles to it, the blank area in each of the spectral lines is disposed in the same relative position. Consequently, all of the lines produced by a given element are readily identifiable at a glance by means of their similarly disposed blank areas.

The next step in the preparation of a master plate involves shifting of the absorbing medium longitudinally of'theslit and spectrum, lines. Then the first known material is replaced with a second known substance which isexcited in the conventional manner; of thesecond substance are superimposed upon the'master plate together with thelines; previouslyformed thereon.

These. newspectral lines will be, interspersed amongthose previously produced on the. plate, but will be readily- The spectral lines' identified by means of the blank area formed in each of the lines. These blank areas are disposed in a position different from the blank areas of the lines produced by the first material. This process is continued until the master plate contains markedspectral lines of as many substances as desired, the lines associated with each substance being readily identifiable by the. position. of their blank areas. After the master plate has been completed, it is inserted in a comparator and projected upon a screen together with an unknown plate in the manner previously described.

One of the principal advantages of the present invention is that the process of analyzing an unknown plate is considerably simplified and expedited. Furthermore, the techniques which must be mastered by an operator are greatly reduced. In fact it has been found that by using spectrographic plates of the present invention a less skilled operator can perform in a few hours a complicated analysis which would require a highly skilled spectroscopistalmost a week to perform using conventional master plates.

Another advantage of the present invention is that the apparatus employed for producing the spectrographic plates is of simple construction and can readily be incorporated into existing or new spectrographs. Furthermore, the exact construction of the apparatus isflexible so that it can be used in conjunction with spectrographs ofmany diverse types.

These and other advantages of the present invention will be more readily apparent from a consideration of the following detailed description of the drawings illustrating a preferred embodiment of the invention.

Figure l is a diagrammatic top plan view of an astigmatic spectrograph having a modified Rowland circle mounting and embodying a spectrum line marker.

Figure 2 is a diagrammatic cross sectional view of a stigmatic prism spectrograph including a spectrum line marker.

Figure 3 is a diagrammatic cross sectional view' of a camera particularly adapted for use with a Rowland circle' type. mounting and embodying a spectrum line marker.

Figure 4 is a horizontal cross sectional view of'the camera shown inFigure 3.

of spectrumline marker;

Figure 6: is an elevational view of a slit construction embodying spectrum line marking-means.

Figure 7i'is a view of a spectrographic plate prepared" in accordance with the present invention.

The drawingsrillustrate the manner in which the spectrum line marking means of this invention can be in-- corporated into two different types of spectrographs. There are obviously many additional types of spectrographs not illustrated. However, from the foregoing description of the general principles of the-present invention and from the following disclosure of several, of its embodiments, those skilled in the art will readily comprehend the various modifications to which the present spectrum line marker is susceptible so that it may be incorporated into any type of spectrograph in use.

As shown diagrammatically in Figure 1, a spectrograph 10 having a modified Rowland circle type of'mounting comprises a central support '11 including a circular mounting ring 12, upon which a ruled concave grating 13, a camera 14, and a slit member 15 are movably mounted. Central support 11 also. carries a pivotally mounted arm 16 carrying condensing lens 17' andspectrum line marking device 18. The material exciting means 20 is shown diagrammatically as a carbon electrode. disposed in alignment with the concave grating, slit and condensing lens. -It will be understood, however, that any suitable exciting means can be employed for vaporizing or exciting the material to be analyzed, such asa low voltage. continuous, electric. arc, a high voltage spark, or a Geissler tube.

The radiations emitted by the material when excited are concentrated by lens 17 upon slit 15. These radiations pass through slit 15 and impinge upon grating 13 by means of which they are dispersed and reflected into camera 14. The camera includes a curved strip of film or a curved photographic plate 21 bent along a curve of a radius equal to the radius of the concave grating, it being understood that the radiation reflected by the concave grating falls into focus along this curve.

The construction and arrangement of the above described parts of the spectrograph are conventional and consititute no part of the present invention. A film obtained by means of such a spectrograph shows a plurality of discreet irregularly spaced lines. These lines are all parallel to one another, and when the film is in the camera, are also disposed parallel to the slit. For the purposes of establishing relative orientation, both the slit and these lines will be referred to as extending vertically. However, it will be understood that by orienting the slit in a horizontal plane and rotating the film 90, the lines could actually be obtained in a horizontal plane.

In order to modify a spectrograph of the type shown in Figure 1 to incorporate line marking means in accordance with this invention, a narrow strip of radiation absorbing or deflecting material is placed in the optical path of the radiations emitted by the source, intermediate their origin and the point of their impingement upon the film. One preferred form of line marking means is shown in Figure 3 in which the marking means are incorporated into the camera and are disposed directly in front of the film. Alternatively a separate line marking device 18 can be placed intermediate the condensing lens and slit member along a line drawn tangentto the center of the film, as shown in Figure 1.

One form of line marking device, particularly adapted to be placed between the condensing lens and slit member, is shown in Figure 5. As there shown, the line marking device 18 comprises a housing 22 having a generally rectangular opening or window 23. Two vertical guideways 24 are provided along the vertical edges of the window and a generally rectangular frame 25 is slidably mounted within the housing in cooperative engagement with guideways 24.

Frame 25 supports a sheet of transparent material 26 such as quartz, glass, cellophane, Celluloid, or the like. The choice of the particular material depends primarily upon the region of the spectrum in which the spectrographer is most interested. That is, these materials are not equally transparent to all wave lengths of radiation. In the ultraviolet region, Celluloid and quartz make particularly satisfactory material since they are very permeable by this type of radiation. Glass is very satisfactory material, in both the visible region of the spectrum and in the infrared region.

A narrow marking strip 27 extends across the transparent material at right angles to the guideways 24 and slit 15. This strip functions to absorb or defiect any radiations impinging upon it; and can be formed in any suitable manner such as by grinding a narrow groove in the transparent sheet material and filling the groove with India ink, absorbing dye, black paint, a metallic strip, etc. It is also contemplated that a metallic wire or other structurally rigid member can be used to form the marking strip. In such an embodiment the transparent material can be eliminated entirely and the metallic wire stretched across the frame and soldered or otherwise secured to its vertical side members.

Means are provided for raising and lowering frame 25, thereby shifting marking strip 27 longitudinally of the slit. These means comprise a spring 30, one end of which is disposed within recess 31 provided in the bottom of housing 22; and the other end of which bears against the lowermost edge of frame 25 and is held in position by a pin 32 secured to the frame. A positioning screw 33 threadably engages an opening in housing 22 and includes a tip 34 cooperating with a socket provided in boss 35 formed on the top edge of the frame. Knob 36 is secured to the outermost edge of screw 33 for threading the screw in and out to raise or lower frame 25 and marking strip 27, it being understood that spring 30 is effective to urge the frame into engagement with tip 34 of the positioning screw at all times. Frame 25 is also provided with a pointer 37 mounted on one vertical edge of the frame. The pointer moves over a graduated scale 38 carried by housing 22. By means of the registry of the pointer with various markings on the scale, marking strip 27 may be adjusted to any desired vertical position.

Figures 3 and 4 showa camera construction adapted for use with a spectrograph of the type shown in Figure l. The camera 4!) is provided with line marking means disposed interiorly of the camera housing 41. Thus a spectrograph including such a camera is adapted to produce master spectrographic plates in accordance with the principles of this invention without theneed for a separate line marker 18 of the type shown in Figures 1 and 5. More specifically, the camera 40 comprises, in addition to housing 41, film holding means 42 and guides 43 for supporting the film along an arcuate curve having the same radius of curvature as the concave grating. Camera 40 could, of course, include means for supporting a photographic plate other than a film if desired. In the embodiment shown, a lens 44 is mounted in a lens opening 45 in the front of the camera and directs light passing through the opening onto the film or plate. It will be understood however, that this lens may be omitted as it is in many spectrographic cameras.

The line marking means 46 provided in the camera include two bearing blocks 47 soldered or otherwise secured to the interior of housing 41 adjacent opposite side walls thereof. Each of the bearing blocks 47 is provided with a vertical bore for receiving a rod 48. Rods 48 carry the ends of the inverted, generally U-shaped, frame 49 including upright members 50 and cross member 51. The line marking strip 52, as shown, is constituted by a wire stretched between vertical frame members 5050. The wire is clamped, soldered or otherwise secured to the frame in such a manner that the wire extends longitudinally across the film 53 at right angles to the transverse spectrum line images indicated by light lines 54. As shown particularly in Figure 4, wire 52 is sufficiently rigid so that it maintains an arcuate configuration concentric with that of the film, the wire being disposed adjacent to the front face of the film.

Cross member 51 is joined as by soldering to a tie rod 55 which extends vertically through an opening in the housing provided with a light seal and bearing member 56. Tie rod 55 is associated at its outer end with raising and lowering means 57 by means of which frame 51, and marking strip 52, may be adjustably positioned within the housing. Any suitable mechanism may be provided for raising and lowering the tie rod; the means illustrated include a rack 58 mounted on the end of the tie rod and adapted for cooperative engagement with a pinion 59 mounted on shaft 60 which is in turn carried by bracket 61. A knob 62 is also mounted on shaft 60 for rotating the pinion and raising or lowering the rack, tie rod 55, and frame 46. A pointer 63 is preferably secured to rack 58 and is disposed for registry with graduated scale 64 carried by bracket 61, the pointer and scale providing means for bringing the marking strip into any desired vertical position.

As an alternate marking strip construction to the one shown, a thin blank of quartz or other transparent could be ground or otherwise shaped to conform substantially with the curvature of the Rowland circle of the spectrograph. The transparent material can be marked by forming a groove in it and filling the groove with an absorbing or deflecting material such as paint, India ink,

etc., as described above.

Figure 2 shows a stigmatic prism spectrograph equipped with a line marking device of the type shown in Figure 5. As shown spectrograph 7.0 includes an elongate housing. One side Wall of the housing is provided with an opening 71. Substantially all of this opening is covered by slit member 72, the member being configurated to form a narrow vertical slit 73. A second opening 74 is provided in oneend of the housing for communication with camera 75. The camera supports a film, or photographic plate 7.6 in a horizontal plane angulated with respect to the longitudinal axis of the housing.

Afirst prism 77 is disposed within the housing adjacent slit 73. This prism functions to direct the light rays entering through the slit onto collimating lens 78 from whichthey pass onto dispersing prism 80. This prism is constructed of glass or preferably of quartz and is effective to disperse the light rays impinging upon it and reflect them backthrough lens 78 into the opening of camera .75. In addition to these elements a material vaporizing or exciting means, diagrammatically indicated by carbon electrode 81, is disposed exteriorly of housing 70 in alignment with prism 77 and slit 73. This exciting means may be of any suitable type including a continuous arc, spark, or Geissler tube as mentioned above. Disposed intermediate exciting means 81 and slit '73 is a condensing'lens .82, the function of which is to concentrate a portion of the radiations emitted by the substance being vaporized and direct them onto slit 73. Line marking device 83 is interposed between the con densing lens 82 and slit member 73, preferably in juxtaposition with the latter. One form of line marking means is shown in Figure and it will be understood that the means are arranged relative to slit member 73 so that marker strip 27 extends across the slit and can be adjusted longitudinally thereof by turning knob 85.

Another type of line marking device especially adapted for use with a spectrograph of the type shown in Figure 2 is illustrated in Figure 6. As there shown, the line marking element 86 is formed integral With the slit defining members 8787. More specifically, when using the line marking means shown in Figure 6, conventional slit member 73 is removed from the spectrograph together with line marker 83. The slit marker is replaced with a slit assembly 88 shown in Figure 6.

Slit assembly 88 comprises two slit defining members 8787 having their inner edges 90 disposed in spaced parallel relationship to define slit 91 through which the rays of light are passed as they enter the spectroscope housing. Assembly 88 is provided with two vertical guideways 92 and 93 for maintaining members 87t57 in parallel alignment, these members being adapted for longitudinal movement along the guideways.

One of the slit members is provided with a projection 94 which extends completely across slit 91 into contact with the opposite slit defining member 87. The position of this line marking projection M relative to the slit can readily be adjusted by means of set screw 95 which threadably engages housing 88 and abuts the slit defining member 87 carrying the projection. The slit defining member also includes an aligning pin 97 extending through an opening in housing 38. A helical spring 98 surrounds pin 97 and is compressed between the inner surface of wall 160 and the top edge of member 87. The spring is effective to continuously urge the member downwardly into engagement with set screw 95, but is yieldable so that the member can be raised against the spring pressure by turning knob 201. In the preferred embodiment the opposite slit defining member 87 is also adjustably positioned within the housing 88; the construction of the positioning means for that member being identical with that of the member just described.

In preparing a master spectrographic plate in accordance with the present invention, the marking strip is disposed in a predetermined position within the optical path of any radiations passing from the exciting means to the photographic plate. That is, the marking strip is adjusted so that its heightrelative to the slit or the photographic film is such that it will absorb or deflect a narrow band of the radiations, blocking out a portion of each of the spectral lines formed on the plate. After the marking strip has been positioned, a sample of a known material is vaporized or excited in the spectrograph.

The known substance will emit radiations of its characteristic wave length. These radiations pass through the slit onto the grating or prism by means of which they are dispersed and reflected onto the photographic plate. However, the marking strip absorbs or deflects a narrow band of the radiation passing through the slit and impinging upon the film. As a result each of the spectral lines formed on the photographic plate contains a narrow blank identifying band. Thus, as shown in Figure 7, with the marking strip aligned in the position P the material when vaporized produces a series of parallel spectral lines marked 8;. Each of these lines can subsequently be identified as being caused by that particular material because of the blank portion B formed in each of the spectral lines. It will be noted that each of the blank portions B is formed at precisely the same height relative to the spectral lines.

The next step in preparing a master spectrographic plate is to remove the first known sample from the exciting means, replacing it with a second known material. The marking strip is shifted vertically to a new predetermined position displaced longitudinally of the slit from its previous one. Then the photographic plate already containing the characteristic lines of the first substance is again exposed. As a result the characteristic spectral lines of the second substance are superimposed upon the plate and are interspersed among the lines characteristic of the first substance. Thus, the second substance causes the spectral lines S each of which is marked by a blank spot B corresponding to the line marker position P This process is continued; that is, new substances are inserted in the spectrograph and their spectral lines are superimposed upon the same photographic plate, the marking strip being shifted for each new substance so that the characteristic lines of each substance contain a blank area at a predetermined position spaced from the area where the lines of other substances are marked. In the complete plate shown in Figure 7, a third substance produced the lines S marked by blank portions B caused by the marking stripsjbeing disposed in position P Similarly, a fourth substance produced the lines the marking strip being disposed in position P in which it was effective to cause blanks B to be formed in the spectral lines. While in the particular plate shown the spectral lines of four substances are identified, it will readily be appreciated that, depending upon. the purposes to which the master plate is to be put, a greater or lesser number of substances could be identified.

After the master spectrographic plate has been prepared it is inserted into a comparator and projected along with a similar plate of the unknown sample. One of the lines of the master plate is brought into registry with a corresponding known line on the unknown plate. Other lines on the unknown plate can then readily be identified by means of the corresponding lines on the master plate. For example, suppose that a line on the unknown plate appears in registry with the fifth line from the left on the master plate shown in Figure 7. In order to identify the element in the sample producing this line, the spectroscopist follows down the unknown line onto the corresponding line of the master plate until he encounters the blanked out portion B At this point the spectroscopist can move horizontally across the plate to a legend placed at the edge of the plate at the same height as the blanks B and identifying the substance burned in the spectrograph when the marking strip was in the position P Or alternatively, the spectroscopist may note that the blank space B corresponds to the second highest position of the marking strip and can then refer to a tabulation of the respective marking strip heights and the substances Whose spectral lines are marked with the strip at various heights.

It will be appreciated that if all of the lines on the unknown plate cannot be identified by means of a single spectrographic master plate, additional master plates, having the spectral lines of other elements identified thereon, may be inserted into the comparator and compared with the unknown plate in the same manner as the first master plate was prepared.

Having described my invention, 1 claim:

1. A method of preparing master spectrographic plates in which each of the spectral lines associated with an element is provided with an identifying mark, said method comprising the steps of energizing a known substance in a spectrograph having a slit and a photographic film, disposing a narrow strip of material impermeable to the radiations emitted by said substance in the path of said radiations intermediate the excitation position of said material and the point of impingement of said radiations upon the photographic film, said narrow strip being effective to obstruct the radiation impinging upon a narrow region of said fihn, whereby a narrow blank area is formed in each of the spectral lines associated with said substance, removing said first known substance from said spectrograph, energizing a second known substance in said spectrograph, shifting the narrow strip of radiation impermeable material longitudinally of the slit whereby the material is efiective to obstruct radiations from impinging upon said film along a narrow region spaced from the first narrow region, and superimposing the spectral lines of said second material upon the photographic film.

2. An attachment for spectrographs for employment in the production of master spectrographic plates, said attachment comprising a housing, said housing having a window formed therein, guide means associated with said housing, a movable frame, a sheet of transparent material carried by said frame in registry with said window, a narrow strip of radiation impermeable material carried by said sheet, said strip being disposed transversely of said Window perpendicular to said guides, and means for adjustably positioning said frame relative to said guides.

3. An attachment for spectrographs for employment in the production of master spectrographic plates, said attachment comprising a housing, two slit defining members mounted within said housing, the adjacent edges of said slit defining members being disposed parallel to one another, the edge of one of said members being configurated to form a marking projection extending outwardly from said edge toward the adjacent edge of said second slit defining member, and means for adjustably positioning said marker carrying member relative to the other slit defining member.

4. A method of preparing master spectrographic plates in which each of the spectral lines associated with an element is provided with an identifying mark, said method comprising the steps of energizing a known substance in a spectrograph having a slit and a photographic film, and disposing a narrow strip of material impermeable to the radiations emitted by said substance, perpendicular to said slit, in the path of said radiations intermediate the excitation position of said material and the point of impingement of said radiations upon the photographic film whereby the material is effective to obstruct radiations from impinging upon said film along a narrow region.

5. A camera for use in preparing master spectrographic plates, said camera comprising a housing, a light admitting opening in one wall of said housing, photographic film holding means disposed within said housing, and line marking means carried by the housing, said line marking means comprising a thin strip of radiation impermeable material disposed transversely of said housing adjacent said film holding means, and means for shifting said line marking means in a direction perpendicular to its extent.

6. An attachment for spectrographs of the type having a narrow slit, said attachment being adapted for employment in the production of master spectrographic plates, said attachment comprising a narrow strip of radiation impermeable material, said strip of material having a width corresponding to a small fraction of the length of said slit, means for mounting said strip of material whereby it extends transversely relative to said slit, and means for shifting said strip in a direction perpendicular to its extent.

7. An attachment for spectrographs of the type having a narrow slit, said attachment being adapted for employment in the production of master spectrographic plates, said attachment comprising a narrow strip of radiation impermeable material, said strip of material having a width corresponding to a small fraction of the length of said slit, means for mounting said strip whereby it extends transversely of said slit, means for shifting said strip in a direction perpendicular to its extent, and scale means for indicating the position of said strip.

8. An attachment for spectrographs for employment in the production of master spectrographic plates, said attachment comprising a housing, said housing having a window formed therein, guides associated with said housing, a movable frame, a narrow strip of radiation impermeable material carried by said frame in registry with said window, said strip being disposed transversely of said window perpendicular of said guides, and means for adjuastably positioning said frame relative to said guides.

9. An attachment for spectrographs for employment in the production of master spectrographic plates, said attachment comprising a housing, two slit defining members mounted within said housing, the adjacent edges of said slit defining members being disposed in parallel spaced relationship relative to one another, the edge of one of said members being configurated to form a narrow projection extending outwardly from said edge into juxtaposition With the adjacent edge of said second slit defining member, and means for adjustably positioning said projection carrying member relative to the other slit defining member.

References Cited in the file of this patent UNITED STATES PATENTS 1,526,504 Rabi Feb. 17, 1925- 2,043,053 Martin June 2, 1936 2,179,657 Estey Nov. 14, 1939 2,309,301 Burr Jan. 26, 1943 OTHER REFERENCES Harrison et al.: Practical Spectroscopy, published i1101948 by Prentice-Hall Inc., New York city, pages 101, 1 2.

Nachtrieb: Principles and Practice of Spectrochemical Analysis, 1st ed., published in 1950 by McGraw- Hill Book Co., Inc., New York, page 232.

Baly: Spectroscopy, vol. 1, 3rd ed., published in 1924 by Longmans, Green & Co., New York, page 46.

Hardy and Perrin: The Principles of Optics, 1st ed., published in 1932 by McGraw-Hill Book Co., Inc., New York, pages 558-559.

Bausch & Lomb Optical 00.: Instruments for Spectrographic Analysis, copyrighted in 1932, pages 15, 16, 17.

Von Arx: A Grating Spectrograph for Use in Qualitative Analysis," pages 407-410 in Journal of Chemical Education, September 1942. 

